1. Field of the Invention
The present invention relates to a method of purifying water and to a water purification system. More particularly, the invention relates to a method and system for the purification of water for a variety of applications including the preparation of drugs, as drinking water, and for use in administering medical care and in the food industry, in the precise electronic industry and for physical and chemical experiments.
2. Description of the Prior Art
In a variety of applications such as those described above, it is essential that water be available which is free of such materials as colloidal substances, bacteria, pyrogens and harmful organic substances. In order to obtain purified water, such conventional methods and systems as distillation, ultrafiltration and reverse osmosis are being used. However, these systems to be most efficient should be employed on a large scale, and the high operating costs of these systems are a serious problem. Further, these methods and systems are frequently inadequate for obtaining clean water in necessary amounts. Moreover, it is essential that the clean water used in the medical care of people should not contain any bacteria and should be free of pyrogens. Pyrogen is a generic name for pyrogenic substances such as the metabolites of bacteria, fungi and yeast, which are defined as substances which induce exothermal reactions in an organism upon injection. Chemically, pyrogens are said to be heat-resistant, high molecular weight complex glycolipids containing nitrogen and phosphorous, and are of a particle size of 1-5 m.mu. and are water-soluble. Pyrogens in micro-amounts of about 0.01 .mu.g/kg are reported to induce pyrogenic reactions in an organism. Pyrogens entering an organism such as by injection into the blood, by infusion-solution, drugs, and the like will cause such side effects as fever or shock. Accordingly, the water which is used for medical care should be germless and pyrogen-free. However, pyrogens cannot be removed from water or be destroyed by the bacteria-filtering method or the high-pressure steam-sterilizing method. Thus, specialized water-treating methods must be used to obtain pyrogen-free water. Moreover, the presence of harmful substances in the low molecular weight organic compounds present in water in small amounts besides bacteria and pyrogen, is further reason for the thorough purification of water. In terms of the present invention, a "small amount" means amounts in the ranges of parts per billion (p.p.b.) and parts per trillion (p.p.t.).
It is particularly desirable to be able to efficiently remove such organic compounds as phthalate esters (dibutyl phthalate, dioctyl phthalate, and the like), straight-chain dibasic acid esters (dioctyl adipate, dioctyl azelate, dioctyl sebacate, and the like), other higher fatty acid esters, higher-fatty acids, and other halogenated benzenes which are present in water in amounts of from several p.p.t. to hundreds p.p.t. As mentioned above, there are many organic compounds which are hardly soluble in water, and are therefore present in minor amounts in water, and yet, such organic compounds are found to be increasing in concentration in river water and underground water year after year around concentrated population centers, in cities and industrial areas. Therefore, a need continues to exist for a very efficient method and system for the removal of the above compounds from water because of the unfavorable circumstances from the hygienic viewpoint of the presence of such organic compounds in tap water and well water.